Re: Help Me Understand Why I'm Getting a Bad Query Plan

Brian,

> I hate to nag, but could anybody help me with this? We have a few
> related queries that are causing noticeable service delays in our
> production system. I've tried a number of different things, but I'm
> running out of ideas and don't know what to do next.

For some reason, your first post didn't make it to the list, which is
why nobody responded.

>> I've got a query on our production system that isn't choosing a good
>> plan. I can't see why it's choosing to do a sequential scan on the
>> ItemExperienceLog table. That table is about 800mb and has about 2.5
>> million records. This example query only returns 4 records. I've
>> tried upping the statics for ItemExperienceLog.VistorId and
>> ItemExperienceLog.ItemId to 1000 (from out default of 100) with no
>> success.

Yes, that is kind of inexplicable. For some reason, it's assigning a
very high cost to the nestloops, which is why it wants to avoid them
with a seq scan. Can you try lowering cpu_index_cost to 0.001 and see
how that affects the plan?

--Josh